Voltage on 1st cap goes slightly over 500V when on stdby... dangerous?

[Hardtailed]

I built my Marshall clone the Marshall way, with the stdby switch between the first cap and the choke/OT CT.

When on, the B+ is about 480V, it sounds lovely (albeit freaking loud!) so that's perfect for me.

But on the STDBY, the voltage on that first cap (a JJ 50/50 cap can, rated at 500V) jumps to about 504-505V.

How much of a risk am I taking?

Been playing this amp for a few months now no problem, but I'm somewhat afraid of leaving it on standby between sets, I actually just leave it on with the volume on my guitar turned down.

I'm guessing this voltage rating is not exactly rocket science and there has to be a certain tolerance...

[tedmich]

sounds like a nice build, the voltage rating is always a function of expected life time of the cap, temperature etc.
(a handy calculator is here: Illinois Capacitor, Inc. - aluminum electrolytic, metalized film, igbt, power film, organic semiconductor)

So a conservative lifetime of 1000h at 105C and 500VDC lasts MUCH longer at 50C, but about the same at 105C/510VDC; voltage has a much smaller effect than temp.

having the can cap away from hot tubes is good insurance

you should be AOK

[Hardtailed]

Originally Posted by tedmich

sounds like a nice build, the voltage rating is always a function of expected life time of the cap, temperature etc.
(a handy calculator is here: Illinois Capacitor, Inc. - aluminum electrolytic, metalized film, igbt, power film, organic semiconductor)

So a conservative lifetime of 1000h at 105C and 500VDC lasts MUCH longer at 50C, but about the same at 105C/510VDC; voltage has a much smaller effect than temp.

having the can cap away from hot tubes is good insurance

you should be AOK

Thanks for the information!
The caps hardly get warm and the one that's isolated by the standby switch is the one farthest away from the power tubes.
I always switch the mains off first so it can drain off some of its charge and wait about 30 seconds to switch to standby (which is really just a safety measure to not switch the mains on with the standby switch in play position the next time!)

[Enzo]

I wouldnlt worry about it, the caps have a surge rating for just such things.